But during breeding season, especially at dawn, so many birds sing so many melodies in so many voices, however, that instead of a "chorus," the phenomenon seems more like the pre-concert cacophony of every orchestral instrument tuning up and every instrumentalist warming up.

Scales. Trills. Repeated tricky passages. In different keys. From different symphonies. At different tempos. Simultaneously.

Just as each orchestral instrument contributes unique sound, so each bird bestows his unique melody, tone, pitch and rhythm to the symphony.

Recognizing birds by song adds to birdwatchers' pleasure, especially since we often hear a bird before we see him. Song leads us to look.

Generally, only males sing. Some pairs, however, like cardinals and Carolina wrens, serenade one another. While cardinals sing multiple melodies, a common carol is a clear "purdy, purdy, purdy." Most books claim Carolina wrens burst forth with a loud, ringing "teacher, teacher, teacher," but to me their more common chant says "hickory dickory dickory dock."

Most pairs murmur sweet nothings to each other in the form of chips and churrs — except among birds the "nothings" are really more likely assurances: "All is well, and I'm here for you."

After their seven-month absence, I forget their signature solos. So a rapid "sweet, sweet, sweet, little-more-sweet" should tell me a yellow warbler has returned, and a rolling "zee-zee-zee-zoo-zee" should trigger my memory of black-throated green warbler. But each year, I need a refresher course.

What refresher course? Or, better yet, how do we learn bird songs in the first place?

Bird song CDs, available from bookstores and online, let you play and replay identified calls. Load the "music" on your iPod and listen while you drive, mow the lawn or relax. To aid recognition, some CDs add narrative or group similar songs.

Online sites, especially www.allaboutbirds.org/, post audio of every North American bird's song and call, accessed bird by bird. An app for your cellphone does likewise. Some field guides to birds include bird-by-bird audio, often accessed via bar-code reader.

Or, skip the gadgets.

In the wild, watch birds carefully, listening as they sing, connecting bird to song. Educators suggest that by tapping visual and auditory skills simultaneously, you'll likely be most successful.